DESCRIPTION

closelog()
closes the descriptor being used to write to the system logger.
The use of
closelog()
is optional.

openlog()
opens a connection to the system logger for a program.
The string pointed to by
ident
is prepended to every message, and is typically set to the program name.
If
ident
is NULL, the program name is used.
(POSIX.1-2008 does not specify the behavior when
ident
is NULL.)

The
option
argument specifies flags which control the operation of
openlog()
and subsequent calls to
syslog().
The
facility
argument establishes a default to be used if
none is specified in subsequent calls to
syslog().
Values for
option
and
facility
are given below.
The use of
openlog()
is optional; it will automatically be called by
syslog()
if necessary, in which case
ident
will default to NULL.

syslog()
generates a log message, which will be distributed by
syslogd(8).
The
priority
argument is formed by ORing the
facility
and the
level
values (explained below).
The remaining arguments
are a
format,
as in
printf(3)
and any arguments required by the
format,
except that the two character sequence
%m
will be replaced by
the error message string
strerror(errno).
A trailing newline may be added if needed.

The function
vsyslog()
performs the same task as
syslog()
with the difference that it takes a set of arguments which have
been obtained using the
stdarg(3)
variable argument list macros.

The subsections below list the parameters used to set the values of
option, facility, and priority.

option

The
option
argument to
openlog()
is an OR of any of these:

LOG_CONS

Write directly to system console if there is an error while sending to
system logger.

LOG_NDELAY

Open the connection immediately (normally, the connection is opened when
the first message is logged).

LOG_NOWAIT

Don't wait for child processes that may have been created while logging
the message.
(The GNU C library does not create a child process, so this
option has no effect on Linux.)

LOG_ODELAY

The converse of
LOG_NDELAY;
opening of the connection is delayed until
syslog()
is called.
(This is the default, and need not be specified.)

LOG_PERROR

(Not in POSIX.1-2001 or POSIX.1-2008.)
Print to stderr as well.

LOG_PID

Include PID with each message.

facility

The
facility
argument is used to specify what type of program is logging the message.
This lets the configuration file specify that messages from different
facilities will be handled differently.

level

This determines the importance of the message.
The levels are, in order of decreasing importance:

LOG_EMERG

system is unusable

LOG_ALERT

action must be taken immediately

LOG_CRIT

critical conditions

LOG_ERR

error conditions

LOG_WARNING

warning conditions

LOG_NOTICE

normal, but significant, condition

LOG_INFO

informational message

LOG_DEBUG

debug-level message

The function
setlogmask(3)
can be used to restrict logging to specified levels only.

ATTRIBUTES

For an explanation of the terms used in this section, see
attributes(7).

Interface

Attribute

Value

openlog(),
closelog()

Thread safety

MT-Safe

syslog(),
vsyslog()

Thread safety

MT-Safe env locale

CONFORMING TO

The functions
openlog(),
closelog(),
and
syslog()
(but not
vsyslog())
are specified in SUSv2, POSIX.1-2001, and POSIX.1-2008.
POSIX.1-2001 specifies only the
LOG_USER
and
LOG_LOCAL*
values for
facility.
However, with the exception of
LOG_AUTHPRIV
and
LOG_FTP,
the other
facility
values appear on most UNIX systems.
The
LOG_PERROR
value for
option
is not specified by POSIX.1-2001 or POSIX.1-2008, but is available
in most versions of UNIX.

NOTES

The argument
ident
in the call of
openlog()
is probably stored as-is.
Thus, if the string it points to
is changed,
syslog()
may start prepending the changed string, and if the string
it points to ceases to exist, the results are undefined.
Most portable is to use a string constant.

Never pass a string with user-supplied data as a format,
use the following instead:

syslog(priority, "%s", string);

SEE ALSO

COLOPHON

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man-pages
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A description of the project,
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and the latest version of this page,
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